Volume control for electrical sound reproducer



Jan. 17, 1939. R. H. DREISBACH VOLUME CONTROL FOR ELECTRICAL SOUND REPRDUCER Filed Nov. so, 1956 LEVEL NORMAL Scum: P! SATION Low SOUND LEVEL WW (,OMPEN u9N ca e om/ NV I (News PEYR Secouo INVENTOR.

Rosam- H. DRE/SBACH.

BY W I w TTORNEY Patented Jan. 17, 1939 VOLUME common Fort amcrnicnn somvn nnraonucaa Robert H. Dreisbach, Fort Wayne, Ind., assignor,

by meanenssignments, to The Magnavox Company, Incorporated, Fort Wayne, Ind., a corporation of Indiana 1 Application November 30, 1936, Serial No. 113,445

8 Claims. (01. 179-1) The present invention relates to volume conpick-up having means adapted to compensate for trol means forelectrical sound reproducing apdeficiencies inherent in sound records, paratus and more particularly to a volume control Figure 3 is a modification of the circuit illushaving means which will compensate for the trated in Figure 2, showing an arrangement for 5 varying sensitivity of the human eat at dlfierent rendering the compensating feature more eifecsound levels. tive as the volume of sound is decreased,

An object of the present invention is to provide Figure 4 shows an'arrangement similar to that a new, novel and eiflcient volume control means of Figure 3, with an additional compensating for electric sound reproducing apparatus such as means which is operative in the low frequency radio receivers, microphones and electrical range when the volume control is operating at a 10 phonographs. high sound level,

Another object of the invention is to provide 0 Figure 5 is a diagram showing an arrangement a volume control having a novel arrangement of having all of the advantages possessed by the resistance and capacitance to automatically compreviously illustrated arrangements plus means pensate for the varying sensitivity of the human operative at the higher 'sound frequencieswhen l5 ear at different sound levels. the volume control is operating at a low sound Another object of the invention is to provide a level, and compensating circuit for a volume control means Figure 6 is a chart graphically showing the efwhich will provide a, more .uniform volume refeet of the volume control and compensating sponse at different frequencies and over a wider means at different sound levels. 20 sound frequency range than has heretofore been It w be appare t t a if all Sound Programs possible were reproduced at their original sound level the Another object of the invention is to provide pr duced sound would eifect the human ear in a variable volume control means for use with the same manner as would the sound at the origielectrical phonographs that will compensate for nal source, irrespective of the sensitivity char- 25 the inherent defect which results from the fact acteristics of the human ear. However. since it that the phonograph records are cut at a constant is n t always desirable d/ r f a t r p amplitude below frequencies of 400' cycles in,- duce the sound progra at' e a s und level, stead of at a constant velocity, as is the case at it is customary to provide a volume control d the higher frequencies. vice which may be operated to either raise or 30 It is known that the sensitivity of the human lower the sound level. Since the sensitivity of ear varies throughout the entire frequency range the human ear varies as the sound level is and that the ear is more sensitive to changes in changed. t is desirable a means be provided sound level at the lower and high sound frewith the volume control device to comp quencies. Therefore it is a further object of the for this chan e In sensitivity of the This 35 present invention to provide a suitable compena te st c of t e human ear is Particularly sating means for use in connection with a volume noticeable below a Sound que cy of 400 cycles control device which will automatically compen- P Second and ab ve a Sound frequency of psate for the changing sensitivity of the human pr im y 2000 v pers n For x mp ear at both the high and low sound levels. at the relatively high sound-level the human ear 40 Other objects and advantages of the invention s more Sensitive to frequencies below 400 yc e will be in part pointed out and in art evid nt per second and to frequencies above 2000 cycles to those skilled in the art as the description per Se o than it s o t intermediate range 1 thereof proceeds. frequencies. Conversely at a low sound level the 5 For a better understanding of the invention earisless sensitive to sound frequencies below 400 reference should be had to the accompanying cycles and t0 the Sound frequencies bo pdiagrams which will serve in connection with the p x a y 2000 y s p s d than it s to description to illustrate one embodiment of the the. intermediate range of frequencies. Conseinvention. quently if the overall loudness of the reproduced In the drawing: program is considerably and uniformly increased,

Figure 1 shows a'simple volume controlling deto the observer 'the low and high fr qu vice for use in connection with a piezo-crystal sounds will seem to have been increased out of type of phonographic pick-up, proportion to the overall increase in loudness.

Figure 2 is a diagram similar to Figure 1, show- On the other hand, if the overall loudness of ing a similar arrangement for a phonographic the reproduced music is considerably and unihigh frequency sounds will appear to have been decreased out of proportion to the overall de crease in loudness, and as a result the music in each of these instances will lack the fullness and richness characteristic of a normal reproduction over a wide frequency range.

In accordance with the present invention compensation is provided in connection with the volume control means which will automatically increase the relative intensity of the low and high frequency sounds, with respect to the sounds of the intermediate frequency, when the overall loudness of the reproduced program is decreased by the volume control' means. At the same time the invention also provides a compensating arrangement which will automatically decrease the relative intensity of the low and high frequency sounds, with respect to the sounds of the intermediate frequency, when the overall loudness of the program is increased to a high level by means of the volume control means.

cut with constant amplitude for constant input at sound frequencies below approximately 400 cycles per second rather than at constant velocity, as is the case throughout the remaining sound frequency range. This method of cutting the sound records, unless compensated for, results in a relatively decreased response at the lower sound frequencies, and as a result the response below 400 cycles per second will be substantially proportional to the frequency.

In the remaining description it will be understood that where reference is made to the low frequency sounds, this will include those frequencies up to approximately 400 cycles per second, andthat when the higher frequencies are referred to, this will include those frequencies above 2000 cycles per second. It will be also understood that when reference is made to compensation in either the normal, high or low sound levels, that the compensation made will be with respect to the level established by the intermediate frequency range as a reference point.

Reference is now made to the drawing for a the crystal pick-up, in order that no attenuation of the low frequency voltages will occur.

Figure 2 of the drawing shows the arrangement of Figure 1, with an equalizing circuit, by means of which the higher frequencies are attenuated in such a manner that the overall electrical response from the pick-up I will be relatively flat throughout the sound frequency range from 40 cycles to 8000 cycles when usedwith a phonograph record out in accordance with present practice, wherein all frequencies below approximately 400 cycles are cut at a constant amplitude for a constant input to the record formly decreased, to the observer the low and cutter. This equalizing circuit includes a resistance R2, which is connected in series with a resistor R3 and a capacitor C1 to form a shunt circuit across the output of the crystal pick-up l0. In this arrangement the resistor R1 with its slidable contact H is connected at one side between the resistor R2 and the capacitor C1,

slidable contact 12, by means of which its effective value in the shunt circuit may be varied as the slidable contact II is moved along the resistance R1 to vary the volume of sound. This is accomplished by controlling the slidable contacts II and I2 with a single operating knob or other means, so that when the sound level is increased by an upward movement of the contact ll along the resistance R1, the contact I! will move to the left along resistance R: and gradually cut the resistance R: out of the circuit.

At frequencies above 400 cycles, or any other chosen frequency, the impedance of the capacitor C1 is low with respect to that of resistance Ra, so that the combined impedance of this circuit will be substantially constant for currents from 400 cycles per second up to the highest frequencies encountered in the reproduced sound range. The value of resistance R: is low with respect to the value of the resistance R2, so that with all or a considerable portion of the resistor R: in the circuit, the capacitor C1 and resistor Ra will shunt a considerable portion of the current, decreasing more or less uniformly the voltage of the sound current above1400- cycles per second. In this and the other arrangements the value of the capacitor C1 is chosen so that at frequencies below 400 cycles its impedance will become important with respect to that of R3, and consequently the lower the frequency the less will be the current which is shunted thereby, and the less the output voltage will be reduced. The overall effect of the capacitor C1 and resistor R: then, with the resistor R2 in the circuit, is to attenuate substantially uniformly all frequencies above 400 .cycles, or some other chosen frequency, and below this frequency, to attenuate less and less as the frequency is reduced. Considered with respect to the high frequencies at a given intensity level, the lower frequencies are raised in sound level, with the amount of raise in sound level increasing as the frequency decreases. In other words, as the level is increased by means of the volume control, and

the resistance R2 is gradually cut out of the circuit, and the impedance of the pick-up alone, or in series with a small portion of the resistance R2, becomes low with respect to the resistance R3, the reduction in voltage ,due to the shunt circuit C1 Ra becomes much less, and as a result the compensating effect described above will become much less, although acting in the same general direction with respect to the soun frequency. v The adjustment of contact ll upon thev resistance R1, which is operated simultaneously with the contact I2 upon the resistance R2, does not of itself change the compensation described above, but merely changes the voltage uniformly without respect to frequency, thus synchronizing the overall loudness control with the frequency compensation mentioned above.

in partial shunt, is large with respect to the im- 1 pedance of the shunt circuit, including the capacitor C1 and the resistor R3. This is particularly true for loudness settings from a low to a maximum or rather high sound level. In volume control adjustments approaching maximum loudness, however, when the relatively low resistance R4 parallels most or all of the resistance R1, the combined resistance of R1 and R1 is relatively low.

, At this setting. the resistance R2 will be largely or completely out outof the circuit, and therefore the voltage at the lower frequencies will be relatively reduced, because the pick-up III, which has a high impedance at low frequencies, will at these frequencies be feeding into an impedance which is low with respect to its own impedance, and also partly because the compensating effect of the shunt circuit, including the capacitor C1 and the resistor R3, will be reduced due to the parallel .low impedance circuit formed by the resistances R1 and R4. The resistance Rl will have substantially no direct effect upon the sound volume at low sound level settings, but will reduce the compensating efiect of the resistance R2 and the shunt circuit formed by capacitor C1 and resistance R3 at the high sound level settings.

The arrangement illustrated in Figure 5 is similar to that just described in connection with Figure 4, with an additional capacitor C2 therein to provide additional compensation in the high frequency range when the volume control is operating at a low sound level. In this arrangement the capacitor C: will have little or no effect at the high volume or loudness settings, as it is at this time shunted/across only a small portion of the resistor R1. At low volume settings, however, it will be shunted across a greater portion of the resistor. R1, or a higher value of resistance. The capacity of the capacitor C215 so chosen that its impedance at high frequencies will be low with respect to that part of R1 which it parallels, although its impedance at low frequencies will still be high with respect to that part of R1 which it parallels. By thus providing a low impedancepath for the high frequencies, the voltage at these frequencies is increased with respect to the voltage at the intermediatefrequencies, and the amount of compensation is increased as the volume control is operated to lower the volume or loudness of the sound.

. In Figure 6 of the drawing there is shown a I series of curves which graphically illustrate the second. In this figure of the drawing, the upper curves represent graphically the effect of loud sound reproduction upon the human ear, both with and without compensation as provided for by this invention at different frequencies, and the lower curve represents the effect upon the human ear, both with and without compensation, at a lowsound level of reproduction. The intermediate curves show the effect produced by the invention in compensating for the deficiency found in phonographic records below sound frequencies of approximately 400 cycles per second, as well as compensation for the varying sensitivity of the ear at the extremes of the frequency range.

As shown in the upper curves, the compensation provided by the volume control means lowers the volume of sound at the extreme ends of the sound frequency scale so that the intermediate range of frequencies will to all intents and purposes be reproduced at substantially the same level or volume as the low and high frequencies, whereas, as illustrated in the lower series of curves, the volume control will function to increase the tonal response at the ends of the sound frequency range, so that the intermediate sound frequency range will to all intents and purposes be relatively somewhat lower than the frequencies at the upper and lower ends of the frequency scale. In connection with the intermediate series of curves, the volume control serves particularly to elevate the volume of the lower frequency sounds and thus compensate for the deficiencies found in phonograph records, as has been heretofore described. At this sound level the higher frequencies are also somewhat elevated so that in effect the sound, while produced at its original and normal volume, will have more fullness and richness of tone throughout the entire frequency range.

It will be understood that the amount of compensation and the manner of variation provided with respect to frequency and with respect to loudness levels can be adjusted over wide ranges by selecting different and proper values for the resistances R1, R2, R3 and R4, and the capacitors C1 and C2, and also by adjusting the coupling between the resistors R1 and R2.

While I have, for the sake of clearness and in order to disclose the invention so that the same "can be readily understood, described and illustrated specific devices and arrangements, I desire to have it understood that this invention is not limited to the specific means disclosed, but

- within the scope of the appended claims are to be considered as part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is- 1. In a sound reproducing system of the character described, the combination of a phonographic pick-up device adapted to generate voltages of sound producing frequencies, a variable volume control resistance connected in shunt across the output of said pick-up device, the impedance of said volume control resistance being high as compared to that of the pick-up device, a second variable resistance in series with the output of said pick-up device, said variable volume control resistance and said second variable resistance being adjustable in unison, and a filter adapted, to attenuate the voltages generated by said pick-up substantially uniformly at all frequencies above 400 cycles per second and in a diminishing manner as the frequency of the sound current decreases, said filter circuit including a capacitance and a resistance connected in shunt across said pick-up device and said second 2. In a volume controlling system for electrically produced modulated currents of sound producing frequencies, the combination of a modulated current source, a resistance in series with said source of modulated current having a variable contact, a volume controlling resistance connected in shunt with said first resistance and said source of modulated current and also having a variable volume controlling contact associated therewith, the variable contacts of said first and second resistances being controllable in unison by a single operating means, a filter circuit including a capacitance and a resistance connected in shunt with'said volume controlling resistance, a low resistance shunt connected between the adjustable contact and one side of said modulated current source to shunt a portion of said volume controlling resistance, and a capacitor connected between the adjustable contact upon said volume controlling'resistance and the other side of said modulated current source to operate in shunt with a portion of said volume controlling resistance.

3. In a volume controlling system for electrically produced, modulated currents of sound reproducing frequencies, the combination of a modulated current source, a volume controlling resistanceconnected in .shunt with said source of modulated current and having a variable volume controlling contact associated therewith, a filter circuit including a capacitance and a resistance connected in shunt with said volume controlling resistance, a low resistance shunt connected between the adjustable contact of said volume controlling resistance and one side of, said modulated current source to shunt a portion of said volume controlling resistance, and a capacitor connected to the adjustable contact of said volume controlling resistance and the other side of said modulated current source, whereby said low resistance and said capacitor will operate in shunt with varying portions of said volume controlling resistance as its slidable contact is moved thereover.

4. In a volume controlling system for electrically produced modulated currents of sound reproducing frequencies, the combination of a modulated current source, a variable resistance in series with said source of modulated current, a volume controlling resistance connected in shunt with a portion of said variable resistance and said source of modulated current and having a variable volume controlling contact associated therewith, a filter circuit including a capacitance and a resistance connected in shunt with said volume controlling resistance, a low resistance shunt connected between the adjustable contact and one side of said modulated current source to shunt a portion of said volume controlling resistance, a capacitor connected between the adjustable contact upon said volume controlling resistance and the other side of said modulated current source, whereby it will operate in shunt with a portion of said volume controlling resistance, and a means for simultaneously adjusting the value of said variable resistance and said volume controlling resistance.

5. In a volume controlling system for electrically produced modulated currents of sound reprohaving an adjustable volume controlling tap associated therewith, a filter circuit including a capacitance and a resistance connected in shunting relation with said volume controlling re sistance, and a low resistance shunt connected between the adjustable tap of said volume controlling resistance and one side of said modulated current source operatingto shunt a portion of said volume controlling resistance, whereby said low resistance will operate in parallel with varying portions of said volume controlling resistance as its adjustable tap is moved thereover.

6. In a compensated volume controlling system for the attenuation of modulated sound currents to produce a uniform level of response over a wide range of frequencies, the combination of a modulated current input source having capacitive reactance, a volume controlling resistance connected in shunt across said input source and having a variable output control contact associated therewith, the total resistance of said volume controlling resistance being high as compared to the impedance of the capacitive input source at low frequencies to avoid attenuation at the low frequencies, and a low resistance shunt connected to parallel with varying portions of said volume controlling resistance as determined by the adjustment of its variable output control contact, whereby the effective value of said volume controlling reslstance will be decreased at the higher sound volumes.

7. In a compensated volume controlling system for the attenuation of modulated sound currents to produce a uniform response over a wide range of frequencies, the combination of a sound record having a uniform amplitude of cutting, a crystal pick-up device cooperating with said sound record and having capacitive reactance. a volume controlling resistance connected in shunt across said pick-up device having a variable output control contact associated therewith, the total resistance of said volume controlling resistance being high as compared to the impedance of said crystal pick-up device at low frequencies to avoid attenuation at the low frequencies, and a low resistance shunt connected to parallel with varying portions of said volume controlling resistance as determined by the adjustment of its variable output control contact, whereby the effective value of said volume controlling resistance will be decreased at the higher sound volumes.

8. In a compensated volume controlling system for the attenuation of modulated sound currents to produce a, uniform level of response over a wide range of frequencies, the combination of a modulated current input source having capacitive reactance, a volume controlling resistance connected in shunt across said input source and having a variable output control contact associated therewith, the total resistance of said volume controlling resistance being high as compared to the impedance of the capacitive'input source at low frequencies to avoid attenuation at the low frequencies, a low resistance shunt connected in parallel with varying portions of said volume controlling resistance as determined by the adjustment of its variable output control contact, and a capacitance connected in series with said low resistance shunt and operating in parallel with the remaining portion of said volume control resistance as determined by the adjustment of its variable output control contact.

ROBERT H. DREISBACH. 

